Chemical vapor deposition (CVD) diffusion furnaces are operative to deposit thin-film of selected material on vertically oriented planar semiconductor wafers during the various phases of integrated circuit fabrication. Reactant gas injected into the diffusion furnace pyrolytically reacts and is surface catalyzed to deposit selected thin-film in solid phase on the vertically oriented wafers. In many CVD deposition processes, such as the so-called low pressure photochemical and low pressure photosensitized processes, a phenomenon occurs where the reactant gas is surface catalyzed at the multiple boat-wafer contact points to deposit thin-film in solid phase on the boat to the exclusion of the wafers. The effective zone of depletion extends in many instances over a much greater spatial region than that defined by the actual spatial region physically adjacent the multiple contact points of the individual wafers with the boat, thereby producing wafers having unacceptably non-uniform thin-film deposits. One known technique to eliminate this phenomenon is to array the semiconductor wafers horizontally in a common plane on a support surface. In this manner, reactant gas is surface-catalyzed by an effectively uniform surface so that competition between the support surface and the wafers for the reactant is thereby obviated. However, among other disadvantages, system throughput capability is materially limited, since only a comparatively small number of semiconductor wafers can be horizontally arrayed in a diffusion furnace at one time. A further disadvantage to this approach lies in the fact that particulates generated during the deposition process by necessity fall onto the horizontal wafer surfaces.